1. Field of the Invention
This invention relates to a magnetic Fe oxide powder suitable for producing a magnetic recording member having stable magnetic properties resistant to mechanical pressure and impact, and more particularly to a magnetic Fe oxide powder suitable for producing a magnetic recording member having less coercive force ageing, especially a magnetic Fe oxide powder including Co or like divalent metals (hereinafter designated as Co) and having a high magnetic anisotropy and coercive force.
This invention also relates to a process for producing the magnetic Fe oxide.
2. Description of the Prior Art
A Co containing magnetic Fe oxide powder is already known for producing a magnetic recording member, which is obtained by adding Co to a magnetic Fe oxide. The coercive force of the Co-containing Fe oxide powder is high and the resulting recording member can be used for high density recording. Methods of adding Co to Fe oxide are disclosed, for example, in Japanese Patent Publication Nos. 15638/60, 10994/73, 6538/66 and U.S. Pat. No. 3,573,980.
When a Co containing .gamma.-Fe oxide powder or a Co containing magnetite is formed into a magnetic tape or a like magnetic recording body, the resulting magnetic recording member is magnetically unstable to mechanical pressure and impact. That is to say, the information and signals recorded on the magnetic recording member are weakened by mechanical pressure and impact. Accordingly, where the recorded tape is played repeatedly, the S/N ratio gradually diminishes. Such a undesirable phenomenon is especially marked in a recording member made from a Co containing magnetic Fe oxide, whereas a recording member made from a usual Fe oxide or Cr oxide does not exhibit this phenomenon as markedly. Such phenomenon was already reported in (1) Akashi et al. Television, 18, p. 767 (1964), and (2) Kuroe et al. Magnetic Recording Research Conference Text, No. MR 72-19 (Sept. 1972).
Studies have been made on improvements in the thermal and mechanical stabilities of Co-containing magnetic Fe oxide. To obtain thermal stability in Co-containing magnetic Fe oxide, metallic ions other than Co ion are added to the oxide. Thus, a Co-containing magnetic Fe oxide exhibiting a low reversible coercive force change in the heated state can be produced (as disclosed, for example, in Japanese Patent Publication No. 12175/68, and Japanese Patent Publication (O.P.I.) Nos. 27298/73, 27299/73). U.S. Pat. No. 3,573,980 discloses a method of producing a Co-containing magnetic Fe oxide exhibiting less magnetization at a high temperature by adding reduced Co to the Fe oxide.
The coercive force ageing and the magnetic stabilities to mechanical pressure and impact have not yet been fully examined. Improvement in these properties of a Co-containing magnetic Fe oxide is an urgent problem to be solved.